In U.S. Pat. No. 4,005,927 and copending applications by E. A. J. Marcatili, Ser. No. 58,744, filed July 18, 1979 and now U.S. Pat. No. 4,251,130, and by P. P. Liu et al (1-61), Ser. No. 161,761, filed June 23, 1980, and now U.S. Pat. No. 4,372,643 both of which are assigned to applicant's assignee, gating circuits of the velocity matched type (VMG) are disclosed. In the patent and the Marcatili application, gating is produced by a traveling electrical modulating signal that propagates in synchronism with an optical signal. These are the so-called "traveling wave, velocity matched gates" (TW-VMG). In the Liu et al application, the electrical circuit is tuned so as to produce a standing electrical wave. However, the two oppositely propagating waves that produce the standing wave are also velocity matched to the optical signal. This class of devices is the so-called "standing wave, velocity matched gate" (SW-VMG).
The general problem with both classes of velocity matched gates resides in the fact that the refractive indices of the substrate material in which the gate is formed are very different at the electrical signal and optical signal frequencies. As a consequence, a special design of the electrical wavepath is required to satisfy the velocity match requirement, and to the extent that the velocities of the signals are not matched, the switching efficiency degenerates significantly.